ABSTRACT This exploratory/developmental study applies social network analysis methods to Medicaid claims data on patterns of multi-provider care received by adults with serious mental illness (SMI). The goal is to identify characteristics of provider networks that are associated with patterns of care for physical health conditions, including quality of care measures and utilization of emergency department and inpatient services. Multiple policy strategies, including health homes and behavioral health based primary care, are currently being pursued to improve the quality of physical health care received by adults with SMI. These strategies directly target networks of care, but studies tend to evaluate them by assessing provider or patient level outcomes. However, systemic improvement is unlikely to occur through replication of a single model across all states and regions. Rather, solutions are likely to depend on characteristics of local or regional provider networks. Despite recent advances in measurement of the quality of behavioral health care, methods for identifying, characterizing and analyzing networks of care for adults with SMI have yet to be developed. This exploratory/developmental project will address this gap by addressing two specific aims. First, we will identify and characterize networks of providers who treat adults with SMI in the Medicaid enrolled population in three states. This will be accomplished using social network analysis methods which infer relationships among providers based on their participation in the treatment of the same patients. Provider networks will then be characterized with respect to common network metrics such as their size (e.g. number of providers), geographic location (urban vs. rural), diversity (number of distinct provider types), density (proportion of patients that are shared), and composition (e.g. includes a hospital or hospital based clinic). This analysis, which will be the first to examine networks of care treating adults with SMI, will produce the basic descriptive foundation for the development of integrated care measures. Second, using the identified networks we will examine associations between network-level measures and the quality of care for physical health conditions and utilization of emergency department and inpatient services. The network-based measures developed in this project will advance research and provide policy-makers with new tools for promoting system integration. This project will thereby improve the effectiveness of efforts to reduce the 8-year disparity in life expectancy faced by adults with SMI. To maximize the impact of this work, detailed specifications of the final measures will be published for public use. Finally, results from this project will enable future research projects to investigate important aspects of health care delivery systems for adults with SMI that have not previously been studied.